ECOPHYSIOLOGICAL CHARACTERISTICS OF PHYTOPLANKTON COMMUNITIES IN A COASTAL AREA OF MEDITERRANEAN SEA (GULF OF NAPLES).

Ecophysiology of phytoplankton was investigated in the Gulf of Naples (Italy) at both spatial and temporal (36 hours cycle) scales in November 1995 and March 1996, in the aim to better characterize the relationships between physical structures and physiological adaptation of phytoplankton. Data obtained will be applied to better interpret and calibrate the water color remote sensing data. Fv/Fmax ratio (indicator of photosynthetic efficiency) and proportions of photoprotective pigments to chlorophyll a (chl a) showed significatively different values in different water masses, such as the Modified Atlantic Water (MAW), or an anticiclonic eddy of offshore origin. Physiology of phytoplankton was also influenced by a convergent frontal system separating the eddy from surrounding waters. Throughout the water column photoprotective reactions were evident in the surface layer (0 – 20 m), while high photosynthetic efficiencies were measured at the bottom of the euphotic zone. Using photoprotectant pigments as tracers we estimated vertical velocities in the sub-surface layer of 0.07 cm/sec and from this inferred kinetic coefficients for ecophysiological processes of light adaptation in the mixed layer. The relevance of such measurements for mesoscale studies and for regional modelling of phytoplankton primary productivity is discussed.